US Secretary of State John Kerry said on Friday it would be a huge mistake if Israel decided to take unilateral military action against Iran over its nuclear programme in the future.

Kerry was asked in an NBC Today show interview if the nuclear deal reached last week between Iran and six world powers would make it more likely that Israel might attempt a military or cyber attack on Tehran.

“That’d be an enormous mistake, a huge mistake with grave consequences for Israel and for the region, and I don’t think it’s necessary,” Kerry said.

On Thursday, Kerry said it is “fantasy plain and simple” to claim that President Barack Obama failed to insist on enough restraints on Iran’s nuclear programme before agreeing to lift economic sanctions long in place.

Republicans were unpersuaded — and said so — at an occasionally contentious Senate Foreign Relations Committee hearing that marked the opening of a new phase in the administration’s drive to prevent Congress from undermining the accord.

“You guys have been bamboozled,” said Senator Jim Risch, a Republican, complaining that the agreement wouldn’t permit neutral testing at Iran’s Parchin military complex to guard against cheating.

The deal, reached earlier this month, will take effect unless Congress blocks it. Republicans in control of the House and Senate hope to do that by passing legislation in September to prevent Obama from lifting sanctions that lawmakers put in place over several years.

Obama has promised to veto any such bill. That would lead to a vote to override his veto, and the administration is searching for 34 votes in the Senate or 146 in the House to assure a veto would stick.

Democrats and allied independents control 46 seats in the Senate, and so far Senators. Dick Durbin, Dianne Feinstein and Martin Heinrich, all Democrcats, have announced support for the plan. In the House, Democratic Leader Nancy Pelosi has expressed optimism that a veto can be upheld.

The hearing unfolded as House Speaker John Boehner hinted at additional steps to stop the deal beyond the legislation, which is expected to be voted on after lawmakers return from an August vacation. “I think there’s a lot of tools at our disposal,” he told reporters, although he did not elaborate.

Given the political calculus, the Senate hearing wasn’t so much an attempt by Kerry to persuade Republicans to support the plan as it was an opportunity to reassure Democrats.

Even so, no matter the objections — and Republicans levelled many in a hearing that stretched until midafternoon — Kerry, Energy Secretary Ernest Moniz and Treasury Secretary Jack Lew were ready with responses.

He also said he expects support for the deal from Saudi Arabia, Iran’s rival in the Middle East. Half a world away, by coincidence or not, Foreign Minister Adel Al Jubair said the agreement appears to have the provisions needed to curtail Iran’s ability to obtain a nuclear weapon. Saudi Arabia and Iran are fierce rivals, and Al Jubeir met separately with Kerry and Obama last week.